@startuml
title Step 3 — Move previous and current

object "Node 1" as n1 {
  value = 1
}

object "Node 2" as n2 {
  value = 2
}

object "Node 3" as n3 {
  value = 3
}

n1 --> "null" : next
n2 --> n3 : next
n3 --> "null" : next

object "previous" as prev
object "current" as cur

prev --> n1
cur --> n2

note right
previous = current
current  = next

The reversed part is now:

1 -> null

The remaining original part is still:

2 -> 3 -> null
end note

@enduml